ATRT-19. RARE EMBRYONAL TUMORS INCLUDING EMBRYONAL TUMOR MULTILAYER ROSETTE, OUTCOME AND PATTERN OF TREATMENT FAILURE: MD ANDERSON CANCER CENTER EXPERIENCE

Rare embryonal tumors (excluding medulloblastoma and ATRT) are aggressive pediatric cancers that include embryonal tumor with multilayer rosettes (ETMR), embryonal tumor with abundant neuropil and true rosettes (ETANTR), and embryonal tumors not otherwise specified (ET-NOS). The presence of driver events like C19MC amplification, DICER1 mutations and other microRNA-related aberrations are vital in diagnostic classification of these tumors. The prognosis of these tumors is dismal despite intensive multimodal treatments with the 5-year overall survival being less than 30%. We retrospectively reviewed 12 patients with rare embryonal tumors who were treated at MD Anderson Cancer Center from 2010 to 2022. Of the 12 patients identified, the mean age at diagnosis was 3.6 years (range: 1-12 years) with no sex differences. Histologically, they were classified into ETMR (4/12), ETANTR (3/12) and ET-NOS (5/12) with C19MC found positive in 2/4 ETMR cases. All patients presented with large infiltrative tumors to the supratentorial (6/12), brainstem (4/12), and spinal (2/12) regions. The majority of patients (10/12) were treated by gross/subtotal resection. Treatment at diagnosis included surgery alone (3/12), surgery with chemotherapy (4/12), surgery with chemotherapy plus radiation (4/12),and chemotherapy plus radiation without surgery (1/12). Five patients reported with de-novo metastasis and 10/12 patients had disease progression at 4.1 months of median follow-up (range: 1.2-10.6 months). Six patients had local recurrence and three patients had local with distant disease at progression. Eight patients are still alive, with 5/8 of them surviving more than 5 years. In conclusion, these rare embryonal tumors are hard to diagnose and treat effectively. Even with successful surgery and intense chemotherapy, almost all of them progress/relapse but combined treatments seem to be effective in a subset of patients. Collaborative multi-institutional efforts are required to define standard treatment approaches and future patient stratification.